Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $56.32   8.338%   $61.016   $61.02   $61.00   $61.00  
  Purchase #2 $227.47   5.683%   $240.3971   $240.40   $240.40   $240.40  
  Purchase #3 $118.99   9.178%   $129.9109   $129.91   $129.90   $129.90  
  Purchase #4 $151.33   8.482%   $164.1658   $164.17   $164.15   $164.20  
  Purchase #5 $28.48   6.865%   $30.4352   $30.44   $30.45   $30.40  
  Purchase #6 $68.33   4.726%   $71.5593   $71.56   $71.55   $71.60  
  Purchase #7 $120.33   6.314%   $127.9276   $127.93   $127.95   $127.90  
  7 purchase totals = $771.25       $825.4119   $825.43   $825.40   $825.40